Great question. Several years ago, I started reading and researching the pig iron industry in the Shenandoah Valley. From my reading, and at present would be hard pressed to provide sources, it seems that in the late 18th and early 19th century. Pennsylvania Dutch miners started exploring the Valley in the Page County area because it looked similar to the area they had mined in Pennsylvania.
They found some good ore sources and the first rendition of Catherine's/Katherine's Furnace was born. Further exploration found more ore sources in Rockingham and Augusta Counties to the South. The town of Shenandoah, VA was particularly rich in raw iron and this area was heavily mined into the early 2oth century. A predecessor of the Norfolk and Western/ Norfolk Southern Railroad built a rail line into this area to transport iron to foundries in the North.
In my younger days I did a fair amount of back country hiking in the George Washington National Forest in South Eastern Augusta County. I have run into several abandoned open pit mines in what is now the Saint Mary's Wilderness Area.
There were also many old iron mines near the town of Buena Vista in Rockbridge County (near Lexington.)
I found a source that said prior to the ACW, Barges were floated down (North) the South Fork of the Shenandoah River with pig iron for the arsenal at Harper's Ferry. If you've seen the Shenandoah River lately that seems hard to believe due to all of the rocks and boulders. I hope this provides some insight into my area.